Recovery of acetone



$5,000. calories per to dilute the acid Patented Aug. 30, 1932 'TATESPATENT ice RECOVERY OF ACETONE No Drawing. Application filed March 7,1929, Serial No. 345,237, and in Great Britain March 14, 1928.

This invention relates to the recovery of acetone from ases containingthe same, and

in particular from air used in drying operations in the production ofartificial silk.

j Hitherto it has been usual to employ either water or cresylic acid asthe absorbing liquid, but the absorptive capacity of these liquids issmall so that, with the amount of acetone usually contained in the airor gases, the final concentration of acetone in the washing liquidisonly a few per cent. With water for example, a concentration of l percent is obtained when theair contains 8.4 grammes of acetone per cubicmetre, and the concentration is only as high as 4 per cent when the air;contains 26.5 grammes of acetone per cubic metre. The absorption withcresylic acid is better than with water, but there are practicaldifficulties in its use and manipula tion.

It has now been found that various solvents which might have beenexpected to be useful are, if anything, less effective than wateritself. In accordancewith the present invention, however, an inorganicacid in a fairly high state of concentration is employed as a solvent toeffect the absorption and recovery of acetone, and by using such asolvent the result is much more satisfactory than either with water orcresylic acid. In particular, fairly concentrated sulphuricacid orphosphoric acid is found to be effective.

' In practice, it is convenient to cause the gases containing theacetone to flow through a series of scrubbing towers, through which theacid employed flows down in' countercurrent to the gases. The absorptionof acetone in strong sulphuric acid gives rise to the evolution of heatamounting to about litre of the acetone absorbed; it'is desirable,therefore, to cool the scrubbing towers. Further, it is desirableinorder that the temperature necessary for distilling off the acetonemay be lower than would be the case if the. acid were maintained in theconcentrated condition.

In order that the carried into effect, an exagain ample of the improvedprocess will now be described in somewhat greater detail.

A series of scrubbing towers are employed, each being enclosed so thatthe air containing the acetone is admitted at the foot of one tower andis taken ofi from the top of the tower without loss, and admitted to thefoot of the next tower, and so forth while the towers are cooled.- Theconcentrated acid which, for example, may be sulphuric acid in 130 Tw.is supplied to the top of the last tower so that the strong acid firstencounters the air from which the greater part of the acetone has beenabstracted. The acid containing some acetone is pumped up by a circulating pump to the head of the last but one scrubbing tower, in whichit takes up more acetone, and from the foot of that tower is pumped upby a circulating pump until it has passed in counter-current with thegases through the whole series of towers.

The saturated acid from the towers is distilled, by which means theacetone is recovered. It is preferred to dilute the acid leaving thetowers to a strength of 95 Tw. and then to fractionate the liquid, whichis heated by steam in a coil or by direct heat, or live steam may beblown into the acid so that the acetone comes off continuously at astrength of per cent by volume. This acetone may then be rectified in aseparate still or concentrating unit. Heat exchangers may be employedwhere convenient to economize in heating and may, for example, take upheat at the point in the cycle where heat is evolved due to absorptionof the acetone by the sulphuric acid, and later by dilution of the acidwith water.

The strength of the acid falls off somewhat during its passage throughthe towers, owing to absorption of moisture from the gases passedthrough the towers when outside air is used. This can be avoided byreturning the dried air free from acetone issuing from the finalscrubbing tower for use in the plant where the acetone is taken up, sothat the same air is continuously circulated throughout the process andhas no opportunity to absorb eX- ternal moisture. If this is not done,the absorption of moisture from the atmosphere willlowor the density ofthe acid, usually about to Tw. As a matter of fact, if

' phosphoric acid isused to absorb the acetone,

ther water before distilling.

. Tw., or even of-a corresponding tonemay be obtained, but, of course,with prothat sulphuric acid of a 0 V ployed, it ispossible to and 40 percent this dilution will generally be suflicient and will renderunnecessary the addition of inr- As regards the densityioi the sulphuricacidto be used, it has already been mentioned strength of 130 Tw. issuitable. When that strength of acidisem of acetone of 10, 20, 30 and 10per cent of the I acid used when the amount of acetone in the air isonly, 1.8, 46,85 and 14.2 cubic metre of air respectively. used of 130VTW.,,125 Tw., 120

grammes per Acid maybe Tw., 115- percentage absorptions of acegresslvely larger proportions of acetone in the air. Thus, wlth acid ofobtained, but in tone in the air needs tobe respectivelyT'Z,

105,209 and 10.5 grammes per cubic metre. f

" With sulphuric acid, it is not advisable to use a higher strengththan130 Tw. it com ,mercial acetone is being dealt withas other: wisesome decompositionfot the acetone occurs. However, this does notapply inthe case of pure acetone, in which case thereis'nodifii- 'culty in usingthe most concentrated 21,010; f Withphosphoric acid, good obtained withconcentrations of 100 and 150 Tw; "With 130 Tw. strength, the absorptionis slightlybetter than'with sulphuric acid of 115 Tw., and withphosphoric' acid of 150- -"Tw. strength, the absorption ofjacetone isbet-;

ter thanwith'sulphuric acid at 130 Tw.

. Sulphuric acid of he concentrations re} ferred to can be -usedinplants employing iron 7 essels and piping, but phosphoric'acid of theconcentrations referred iron,so that the plant for use to above willattack with phosphoric acidis gmorediiiicult and expensive toco'nstruct. Sulphuric acid of 130 118203011060 times as effectiveaswaterin re- Tw. strength "gard to, the absorption of acetone, and asalready mentioned, phosphoric acidnof 150 Twsstrength is found moreeffective, particularlyin obtaining lower concentrations oface tone whendealing with a1r in which it is conftained in the smallerproportionsr Vllhe sulphuric acidmayconveniently be diluted to'a strength of at leastTwl, which is equivalent to 5 0 per cent by weight of acid, but it isnecessary 5130 dilute the sulphuric acid containing :ithe acetone; tonot more than Tw., which is equivalent-to 57 percent by weight ofsulphuric acid in order to avoid decomposition and lossof acetone whichim'ay arise owingtothe highboilingv point-and phuric acid, thereappears'to be always-ave'ry theistrength'of the acid. Withs'ulobtainconcentrations strength of Tw.,

a strength ofill0 ,7 Tun, the concentrations of acetone vor 10, 20, ofthe acid used may be that case the amount of aceresultsmay be smallamount of secondary products formed which are of higher boiling pointthan the acetone, and these amount to 0.5per cent of the acetonerecovered, so that the lossisvery small, and the secondary products are,

themselves capable of being used as solvents.

to occur with f the, necessity of diluting in the case of phosphoricacid simply depends upon whether it is de- No such decomposition appearsphosphoric acid of 130.--TW. Therefore,

sired to keep downl the boiling point during in fact,

the distillation of the acetone, bearing in i mind thatfthe boilingpoint steadily rises with I the increaseof concentration oftheacetone. f

and esters, such as methyl If ethyl alcohol be present in'additionj toor ethyl acetate,

the acetone'to be recovered, the novel process will also result inrecovery of these addi tional bodies, which,h'owever, 7 rated onre-jdistillation, although in the case of the esters some hydrolysismayv occurFafter dilution Y I 7 1 I claim-:-+

.1. A methodof recovering acetonefromgas .7 contain ng same, whichcomprises brlnglng said gas into contact w th an ac d taken from thegroup consisting of sulphuric acid and centration to absorbthe acetone;

phosphoric acid, in a fairly high state'oi' con- 2. A method ofrecovering-acetone fromv :gas containlng from said acid, 1"

are easilysepa,

P95. same,-whichqconsistsinbring; ing said gasi'nto-contact with an acidtaken [from the groupconsi'sting of sulphuricacid Y and phosphoric acid,in a fairlyhigh state of concentration and removing the acetone 99 Am'ethod of recovering, acetone from v gascontainin'g same,

and phosphoric acid, in a which consistsin'br ng- 1 ing said gas into'contactwithian acid-taken "from the group consisting of sulphuric-acid yh gh sta r concentration and removing the acetone from latter at atemperatur belowthatgatjwhich substantialdecomposition sets in;

4;. A' method .ofrecoveringacetone from i which (3011815135 in circugascontain ng same,

[saidacid by "fractional distillation of the lating said gas incountercurrent with an acid 7 taken from-the groupc acidiand phosphoricacid, in a tairlyi high tone from said acid; a

' 5. -A method of i re'covering acetone from acid.

' method. of recovering acetone from gas containing same, which consistsIincirculating said gas in counter-current with I high state of con theacetonefrom said sulphuric acidby distilling the-latter. 7; A methodofre'covering acetone from sulphuric'facid in a fairly centration andseparating with'sulphur'ic acid 7 onsisting of sulphuric V state ofconcentration-andremoving the ace- 1 gas containing same, which consistsin bring 'ing said gas into contact L in a fairly high'istate ofconcentration and.

removing the acetone. fromsaid; sulphuric V gas containing same, whichconsists in bringing said gas into contact with sulphuric acid of adensity of from 110 to 130 degrees Twaddell and removing the acetonefrom said sulphuric acid.

8. A method of recovering acetone from gas containing same, whichconsists in bringing said gas into contact with sulphuric acid in afairly high state of concentration, diluting said sulphuric acid to astrength of at least fifty per cent by weight of acid, and removing theacetone from said sulphuric acid without substantial decomposition ofthe acetone.

9. A method of recovering acetone from gas containing same, whichconsists in bringing said gas into contact with sulphuric acid in afairly high state of concentration, diluting said sulphuric acid to astrength of at least fifty per cent by weight of acid, and removing theacetone from said sulphuric acid by fractional distillation of thelatter at a temperature below that at which substantial decompositionsets in.

10. A method of separating acetone from air bearing acetone and amountsof other solvents which consists in bringing said air into intimatecontact with sulphuric acid in a fairly high state of concentrattion andseparating the acetone from said acid by distillation.

11. A method of recovering acetone from gas containing the same whichconsists in bringing said gas into contact with sulphuric acid of astrength of from 110 to 130 Tw.,

diluting said sulphuric acid to a strength of from 80 to 95 Tw., andremoving the acetone from said sulphuric acid without substantiallydecomposing the acetone.

so In Witness whereof I hereunto subscribe my name this 26th day ofFebruary 1929. 7 WILLIAM REGINALD ORMANDY.

